Elite controllers represent a small group of HIV-1 infected persons who maintain undetectable viral loads in the absence of antiretroviral therapy, and the identification of immune defense mechanisms in these patients with a functional cure of HIV-1 infection is likely to reveal important new information for HIV-1 vaccine design. While prior studies have mostly focused on analyzing classic T- and B-cell mediated immune responses against HIV-1 in elite controllers, very little is known about innate processes that may restrict HIV-1 in CD4 T cells from these patients. Notably, it is well recognized that CD4 T cells from elite controllers are generally permissive to viral infection, but the susceptibility of CD4 T cells to HIV-1 infection in elite controllers as compared to alternative patient cohorts has never been systematically assessed. Moreover, a wide panel of host proteins has been detected in previous studies that can modulate the cellular susceptibility to viral infection, but to what extent such restriction factors are operational in elite controllers remains unclear. Based on strong preliminary data showing that HIV-1 replication is significantly less effectively executed in CD4 T cells from elite controllers, we hypothesize that specific steps of the HIV-1 replication cycle can be identified that are selectively inhibited in CD4 T cells from these patients. To investigate this, we propose a detailed, step-by-step analysis of the viral replication cycle in CD4 T cells from the peripheral blood and lymphoid tissues of elite controllers, and reference populations of progressors or HIV-1 negative individuals (specific aim 1). In our second specific aim, we propose to identify molecular pathways that are mechanistically involved in restricting HIV-1 replication in CD4 T cells from elite controllers by focusing on cyclin-dependent kinase inhibitors (CDKI). These molecules have critical roles in regulating cell proliferation, gene transcription and cell metabolism, but have recently been shown to also act as restriction factors against HIV-1 in hematopoietic stem cells and macrophages. Based on preliminary data showing that specific CDKIs are uniquely upregulated in CD4 T cells from elite controllers, and that their experimental inhibition substantially enhances viral replication in CD4 T cells, we hypothesize that CDKIs represent an innate barrier against viral replication in CD4 T cells from elite controllers that substantially contributes to their ability to maintain undetectable viral loads. To investigate this, we will systematically analyze protein and mRNA expression patterns of these molecules in elite controllers and reference patients, and experimentally analyze how CDKIs interact with viral and host proteins to inhibit viral replication steps (specific aim 2). Overall, these studies have the potential to identify an entirely novel, previously unrecognized mechanism of immune defense in vivo in CD4 T cells from elite controllers, and will provide important new information for clinical strategies to enhance host resistance against HIV-1 infection. PUBLIC HEALTH RELEVANCE: Elite controllers are HIV-1 infected patients who have undetectable HIV-1 replication. The reasons for this spontaneous control of HIV-1 infection are unclear. Here, we will test whether the target cells of HIV-1 in these patients express specific proteins that cause resistance to HIV-1 infection.